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HY-TRAK 100D
SERVICE MANUAL
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COPY NO.
/S~^
DATE S./tQ.te
APPROVED
£)OMNITEST LIMITED
The information contained herein is the
property of and is supplied in confidence
bv Omnitest Limited, and must not be
disclosed or used either in whole or in
part without the written- permission of
the Company
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ISS.l
INDEX
1. SPECIFICATION AND WARRANTY
2. USER GUIDE
3. CIRCUIT DIAGRAMS
4. TEST PROCEDURE
5. ENGINEERING CHANGE NOTES RELEVANT TO HY-TRAK 100D
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ISS.l
1. SPECIFICATION & WARRANTY
1 . 1 Specification
1.2 Limited Warranty
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ISS.l
SECTION 1/PAGE 1
1 . SPECIFICATION & WARRANTY
1 . 1 Specification
Meter Section
Ranges
Accuracy
Measurement Rate
Display
Measurement Technique
200mA 2i% 2 On., 200A
± 2% of reading ± 1 digit
Approx. 3 per second
3i digit LCD
Dual Slope Integration
Audio Section
Ranges
Hy-tone Resolution
Audio Output
Tone Delay
(Open circuit to in-range)
20mA 60mA 6 00mA 6A, 60n
4mA 40mA 400mA 4X1
250mW
<50 milliseconds
General
Max. Voltage between Probe Tips
Open Circuit Probe Voltage
Probes
Probe Isolation from Earth
Overvoltage Protection
Dimensions
Weight
Supply Voltage
Supply Frequency
Power Consumption
Operating Temperature
<20mV for Valid Reading
Clamped to 600mV typical
Removable, 4 wire Kelvin
connected for accuracy
>100KA
to 240V ac
75mm x 220mm x 240mm
(excluding handle)
1.2 Kg
230V or 115V ± 10%
50Hz - 50Hz
12VA
- 70°C
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SECTION 1/PAGE 2
1 .2 Limited Warranty
For a period of 90 days from the date of its purchase new
and undamaged from OMNITEST LIMITED, OMNITEST LIMITED or
its authorised distributors will, without charge, repair
or replace at its option, this product if found by it to be
defective in materials or workmanship, and if returned to
OMNITEST LIMITED or its authorised distributors transportation
prepaid .
This limited warranty is expressly conditioned upon the
product having been used only in normal usage and service
in accordance with instructions of OMNITEST LIMITED and not
having been altered in any way or subject to misuse, negligence
or damage, and not having been repaired or attempted to be
repaired by any one other than OMNITEST LIMITED or its
authorised distributors. With the exception of fuse replace-
ment as specifically detailed herein.
EXCEPT FOR THE FOREGOING EXPRESS WARRANTY OF REPAIR OR
REPLACEMENT, OMNITEST LIMITED MAKES NO WARRANTY OF ANY KIND,
INCLUDING BUT NOT LIMITED TO, ANY EXPRESS OR IMPLIED WARRANTY
OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE, AND
OMNITEST LIMITED SHALL NOT BE LIABLE FOR ANY DAMAGES, WHETHER
DIRECT OR NOT OR OTHERWISE, BEYOND REPAIR OR REPLACING THIS
PRODUCT.
Omnitest Limited pursue a policy of continuous development
and product improvement. The specification in this document
may therefore be changed without prior notice.
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ISS
.1
■
2.
USER
GUIDE
2 . 1 Overview
2 . 2 Operations
2 . 3 Maintenance
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SECTION 2 /PAGE 1
2. USER GUIDE
2 . 1 Overview
The HY-TRAK 100D is the first of a new generation of state of
the art short circuit locators. Its high resolution digital
meter and advanced circuit design ensure an instrument of un-
paralleled performance whilst maintaining an ease of use
suitable to operators at all levels.
Although primarily designed to locate short circuits on
printed circuit boards especially multi-layer, the HY-TRAK
100D is eminently suitable for many other applications which
require an accurate resistance measurement below the range of
standard multimeters. Examples include checking the contact
resistance of relays and switches, measuring the resistance
of coils and motor windings (the HY-TRAK 100D uses a d.c.
injection technique which ensures that there are no errors
introduced by a.c. components) , checking for poor solder or
wire-wrap joints, finding shorted output devices on bus-
structured boards, etc. The instant tone feature of the
HY-TRAK 100D ensures its suitability for continuity checking
of cable harnesses and wire looms.
The operator has the choice of using the meter or the audio
tone to locate the short circuit. The lowest meter reading
or the highest tone indicates the position of the short.
'Dead' shorts (less than 2% of meter f.s.d.) are indicated by
a doubling of the audio tone frequency. This Hy-tone feature
is unique to the HY-TRAK 100D.
The HY-TRAK button introduces a super-sensitive 20 milliohm
full scale tone range to produce sensible tone gradients on
low resistance power tracks whilst maintaining the meter on
200 milliohm range to guarantee legible jitter- free readings.
The d.c. injection (which prevents decoupling capacitors from
introducing 'false' shorts as would be the case on an a.c.
instrument) and the HY-TRAK range ensure that shorts between
voltage planes or power tracks present no problems to the
HY-TRAK 100D, which was specifically designed with this
application in mind.
As both probes are fully floating the HY-TRAK 100D can be used
on earthed equipment without any fear of false readings due to
earth loops.
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ISS.l
SECTION 2/PAGE 2
Warning
Due to the very sensitive DVM input, the HY-TRAK 100D should
only be used on items that are switched off and with all
capacitors discharged .
If the HY-TRAK is connected in error to a voltage source the
internal protection circuitry will prevent permanent damage.
However, it may be necessary to replace certain fuses - see
section 'Fuse Replacement'.
2.2 Operations
(a) Handle Adjustment
Grip the handle arms adjacent to the pivot points and
press inwards. Maintaining the pressure, swivel the handle
to the desired position and release. Handle will now lock
in this position.
(b) Initial Checks
Turn the instrument on via the mains on/off switch incor-
porated in the volume control. The red L.E.D. adjacent
to the volume control should illuminate. A single digit
1 should appear in LCD display if the probes are not
touching .
(If these indications do not appear, check mains supply
and internal 100mA mains fuse.)
Turn volume control fully clockwise. Touch probes together.
A tone should be heard. Adjust volume control to comfor-
table listening level.
The meter should display a reading. (The reading will not
necessarily be zero. See 'Calibration' section.)
(c) Calibration
It is only necessary to calibrate the instrument if precise
resistance readings are required. Normally, when checking
for short circuits, one is looking for the minimum reading,
the actual value is immaterial.
(i) Allow instrument to warm up for 15 minutes with
probes not touching.
(ii) Set to 200 ohm range.
(iii) Short probe tips together.
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ISS.l SECTION 2/PAGE 3
(iv) Adjust 'zero' potentiometer with small screwdriver
to obtain a reading of 00.0 on the LCD display.
There should not be a - sign.
(v) Switch to 20 ohm range. Check reading is 00.0.
(vi) Reading may be typically 1-2 milliohms on 2 ohm
and 200 milliohm ranges due to resistance of probe
tips from Kelvin junction.
Insert probes into calibration resistor sockets on
rear panel. (Ensure instrument is flat on the
bench. )
(vii) Set to 200 ohm range.
(viii) Adjust 'cal* potentiometer to obtain reading of
100.0.
(ix) Remove probes from calibrate resistor sockets.
Short probes together. Check reading is still 00.0.
Your HY-TRAK 100D is now calibrated to within the accuracy
specification .
(d) To Locate a Short Circuit on a P.C.B .
(i) Set to 200 ohm range.
(ii) Connect probes across suspect tracks.
(iii) If tracks are shorted the LCD will display a reading.
Holding one probe steady, move the other along the track
until you obtain the lowest meter reading and highest tone.
You are now very close to the short. Select higher
sensitivity ranges, if required, to precisely locate the
short.
Use the HY-TRAK range on power tracks and earth planes to
obtain a greater sensitivity on the audio range.
(e) Resistance Measurements
Ensure instrument is calibrated. Select appropriate range
and read ohmic value from LCD display. If measuring
suspect solder joints, contact resistance of relays, etc.
do not apply excessive pressure to the probes or you may
affect the resistance of the item under test.
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ISS1 SECTION 2 /PAGE 4
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2.3 Maintenance
This will only be necessary if the instrument has been connected
to a 'live' circuit. (See 'Warning')
(a) Turn instrument off.
(b) Disconnect from a.c. mains supply.
(c) Remove 4 'posidriv' screws from base of instrument. Lift
lid of case.
(d) Remove fuses one at a time and check continuity.
Only replace fuses with correct type and value .
Using an incorrect type or value of fuse will either:
(i) Affect the accuracy of the instrument, or
(ii) Render the overvoltage protection inoperative, or
(iii) Both (i) and (ii) above.
We recommend the Schurter FSF and FST type available from
Messrs Verospeed Ltd., Stansted Road, Boyatt Wood, Eastleigh,
Hants. S05 4ZY.
Part No. 228-23437A 100mA FST
228-23474E 200mA FSF
228-23477G 400mA FSF
Or direct from Omnitest Limited.
The correct value of each fuse is:
Fl 100mA Antisurge Mains
F2 400mA Quick Blow D.C. Inject
F3 200mA Quick Blow Measurement I/P
F4 400mA Quick Blow D.C. Inject
F5 200mA Quick Blow Measurement I/P
(e) Replace lid and tighten 4 retaining screws.
(f) Reconnect to a.c. mains, switch on and verify correct
operation of instrument.
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ISS.l
3. CIRCUIT DIAGRAMS
SHT. 1. Voltage Regulator /Constant Current
SHT. 2. Current Driver Stage
SHT. 3. Differential Input Amplifier
SHT. 4. Audio Section
SHT. 5. Decimal Point Control & L.C.D.
SHT. 6. Power Supply
NOTE:
(a) Sheets 1. through 6. above represent the current
manufactured status of the HY-TRAK 100D.
(b) Sheet 3A represents the details of sheet 3. before
the implementation of ECN 101.
(c) Circuit diagram balloon notation used
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TITLE. POWER SUPPLY.
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ISS.l
4. TEST PROCEDURE
4 . 1 Test Equipment
4.2 Test & Set Up Procedure
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SECTION 4/PAGE 1
4. TEST PROCEDURE
4. 1 Test Equipment
(a) DVM (Typical instrument Fluke 8024B) .
(b) Bench D.C. Variable P.S.U. 0-30v.
(c) Decade Resistance Box.
(d) Test lamps (4 off)
ITEM
1
2
PART (RADIO SPARES)
RS 587-074
RS 423-790
4.2 Test & Set Up Procedure
General
This procedure covers the Test & Setting Up operation for both
issues of the HY-TRAK 100D to date. The essential differences
between the two issues are covered in the associated Engineering
Change Note ECN 101.
The full procedure comprises of 10 stages. It is important to
note that with regard to the two issues of instrument, steps (e)
through (j) are identified as (E) through (J) respectively in
relation to those units produced prior to the issue of ECN 101.
(a) Insulation Tests (Do not connect unit to mains.)
(i) With DVM on 32 MA range:
Check for coOhms between E and N, and E and L mains
terminals.
(ii) With DVM on 320A range:
1. Check between N and L for approx. 190D. (240V
tapping) or approx. 40O-(110V setting).
2. Check for zero Ohms from mains E terminal to
0V link on centre of PCB.
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SECTION 4 /PAGE 2
(iii) Visually check mains tappings and orientation of
transformer. The five plastic lugs on the top
should be facing the rear of the PCB.
(iv) Visually check that capacitor C3 has been removed
from the Anders DPM module.
(v) (ONLY FOR UNITS NOT INCORPORATING ECN 101)
1. Ensure IC5 position has an IC base fitted.
2. Ensure that IC's (741) are fitted to position
IC3/IC4 and IC5. Experience has shown Motorola
devices to give the best operation.
(b) Protection Tests (Ensure that the unit is disconnected
from the mains . )
(i) Remove fuses FS2-FS5. Attach the test lamps across
each fuse position (4 off) .
(ii) Connect probe leads.
(iii) Set PSU (Bench supply) to 10V +.1V.
(iv) Connect PSU -ve to HY-TRAK earth.
(v) Touch one probe tip to PSU +ve, check that two
lights are lit.
(vi) Touch other probe tip to PSU +ve, check that the
other two lights are lit.
(vii) Connect PSU +ve to HY-TRAK earth and repeat steps
(v) and (vi) using PSU -ve.
(viii) Disconnect PSU.
(ix) Replace fuses as follows:
1. FS2 and FS4 with 400mA.
2. FS3 and FS5 with 200mA.
(c) D.C. Voltage Checks
(i) Connect HY-TRAK to mains and turn on: LED should
light.
(ii)
With DVM on DC Volts 32 Volt range, check:
1. Unregulated rails at ±22V ±2V on bridge rectifier
2. ±15V supplies on links at centre of PCB (±0.5V)
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SECTION 4 /PAGE 3
:
3. +4.7V supplies on IC 10 pin 7 & 14 (±1.0V)
(±0.5V)**
4. +0.7V supply on IC 9 pin 16 (±0.2V) (±0.1V)**
** Use these values on units not modified by ECN 101.
(d) D.C. Current Inject Checks
(i) With DVM on DC Volts 3200mV range, connect between
ground and TR3 emitter. (This is L.H. end of large
lQrt resistor at rear L.H. of switch bank.)
Ensure that this voltage can be set to IV (±10mV)
using VR2 (Centre pot at rear of PCB) .
(ii)
With DVM on DC mA 800mA range connect HY-TRAK probes
to DVM probes. You should get:
HY-TRAK
RANGE
READING
ACCURACY
200/1
100UA
±1%
20A
1mA
±1%
2/v
10mA
±1%
200m.fl.
100mA
±1%
HY-TRAK
100mA
±1%
(e) CMRR Adjustment
Not applicable after ECN 101.
(f) Funct ional Checks
(i)
(ii)
(iii)
(iv)
(v)
Short leads together on 20QA. range. Adjust VR3 to
obtain 00.0 on LCD.
Connect test leads to 100a cal. resistor in rear
panel of HY-TRAK. Adjust VR2 to read 100. on 200.O.
range .
Connect HY-TRAK leads to resistance decade box. Set
to lOOn.. Ensure HY-TRAK reads 100.0 ±1.1.
Set Decade box to 0n.
Set HY-TRAK to 'HY-TRAK' range. Ensure reading is
approx . 70 . Om/1 ±2 0mA.
Set to 200mO. range. Ensure reading has not changed.
Set to 2n. range. Ensure reading is .070, i.e.
correlation with reading on 200mn. range ±2 LSD's.
(vi)
Set to 20X1 range , reading should be 0.1.
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SECTION 4 /PAGE 4
1
i
On all the above ranges check correct position of decimal
point.
200mn.
2a.
20/v
200/x
XXX. X
x.xxx
XX. XX
XXX. X
Some leading zeros will be blanked.
(vii) Set Decade box to In. Readings should be:
HY-TRAK
200mTL
2n.
20/1
200TL
Overrange ( 1 )
Overrange
l.xyz
l.xy ±2 LSD'S
1.x ±2 LSD's
(viii) Set to Ida on Decade box. Reading should be:
HY-TRAK
200mn
2/v
2 On.
200-n.
Overrange
Overrange
Overrange
10. xy
10.x
±2 LSD's
NOTE: Some warm up drift may occur over the first 15 minutes
after switch on.
(g) IC5, Select on Test
On 200n range short probes together. Set volume to zero.
Note reading. Turn volume to full. Reading should not
vary by more than three least significant digits, preferably two.
(h) Setting Up Audio Section
Connect HY-TRAK to 1 On. pot.
Set to 20n. range.
(i) Set pot until display reads 6.0.
Adjust VR4 until tone just starting to come in.
Set to 6 . in. - ensure no tone .
Seal VR4 with nail varnish.
(ii) Set pot to 4n, set HY-TRAK to 200n. range.
Adjust VR5 until you just get HY-TONE.
Set pot to 4.2n - ensure no HY-TONE.
Seal VR5 with nail varnish.
(j) R14 S.O.T .
Stay on 200n. range, ensure R14 is 4.7Kn.
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SECTION 4 /PAGE 5
Touch one probe to 0V - you should not get a tone.
Touch other probe to 0V (after removing the first) -
ensure no tone.
If necessary reduce value of R14 until tone disappears for
both the above tests.
(k) Final Checkout
Use the instrument on a PCB. Ensure that HY-TRAK audio
starts at about 20mn.
Ensure that 200ma tone starts at 60mn.
Ensure that HY-TONE starts at 2% of FSD, i.e. 4m/ton 200mn.
range.
Ensure that you get progressive tone slide and that tone
quality is good.
Check ranges all function.
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(E) CMRR Adjustment (BEFORE ECN 101 ONLY)
Disconnect standard HY-TRAK leads. Connect CMRR leads.
Connect to PSU (multiturn side) observing conventional
colour code of polarity. Select PSU 0-1 5V range and set
to 0V ±20mV.
(i) Set HY-TRAK DPM reading to 00.0 (20CUX range) using
VR3 (zero) pot. Set PSU to 1.000V ±50mV.
Set HY-TRAK DPM to 00.0 using VRl (CMRR) pot.
Reset PSU to 0V ±20mV, check HY-TRAK DPM still 00.0.
If not goto (i) and keep repeating procedure until
DPM reads at both 0V and IV.
Seal VRl (CMRR) pot using nail varnish. Remove CMRR leads.
Reconnect standard test leads.
(F) Function Checks (BEFORE ECN 101 ONLY)
(i) Connect standard test leads to 100a cal. resistor
in rear panel of HY-TRAK. Adjust HY-TRAK DPM to
read 100.0 on 20On. range.
(ii) Connect HY-TRAK leads to resistance decade box.
Set to 100n. Ensure HY-TRAK reads 100.0 ±1.1.
■
(iii) Set Decade box to 0n..
Set HY-TRAK to 'HY-TRAK' range. Ensure reading is
approx. 70.0mil±10ma.
(iv) Set to 200mA. range. Ensure reading has not changed.
(v) Set to 2A range. Ensure reading is .070, i.e.
correlation with reading on 200mA range ±2 LSD's.
(vi) Set to 20n range. Reading should be approx. 0.07.
(vii) Set to 200a range, reading should be 0.1.
On all the above ranges check correct position of decimal
point.
200mA
2a
20/v
200n.
xxx. x
x.xxx
xx. xx
xxx.x
Some leading zeros will be blanked.
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ISS.l SECTION 4/PAGE 7
(viii) Set Decade box to La. Readings should be:
HY-TRAK
Over range
(1 )
200mn
Overrange
2a.
1 . xyz
20a
l.xy
±2 LSD'S
200rv
1.x
±2 LSD's
(ix) Set to 100- on Decade box. Readings should be:
HY-TRAK
Overrange
200mA
Overrange
2a
Overrange
20tv
10. xy
200a
10. x
±2 LSD's
NOTE: Some warm up drift may occur over the first 15 minutes
after switch on.
(G) IC3, IC4, IC5, Select on Test (BEFORE ECN 101 ONLY)
On any HY-TRAK range short probes together. Set volume to
zero. Note reading. Turn volume to full. Reading should
not vary by more than three least significant digits,
preferably two.
If it does, try different IC3's, IC4's and IC5*s until you
find a suitable set.
This problem is solved by the implementation of ECN 101.
NOTE: In theory, changing IC3, 4 and 5 should not change
the CMRR setting. In practice, it is worth going
over section (E) (i) again.
(H) Setting Up Audio Section (BEFORE ECN 101 ONLY)
Reconnect HY-TRAK to resistance decade box.
Set to 200a range .
(i) Set decade box to 60ji.
Adjust VR4 until tone just starting to come in.
Set to 6 La - ensure no tone.
Seal VR 4 with nail varnish.
(ii) Set decade box to 4A.
Adjust VR5 until you just get HY-TONE.
Set to 5/1- ensure no HY-TONE .
Seal VR5 with nail varnish.
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SECTION 4/PAGE 8
:
(J) R14 S.O.T . (BEFORE ECN 101 ONLY)
Stay on 200A range .
Connect decade box via croc clip leads, to R14 terminals -
Set to approx. 10KA.
Touch one probe to 0V - you should not get a tone. If you
do, reduce decade box until tone just disappears.
Touch other probe to 0V (after removing the first) .
Ensure no tone. Again reduce decade box if necessary until
tone just disappears.
Note decade box reading.
Connect nearest standard value resistor across R14, (probably
best with E-Z clips first) .
Again touch probes to 0V and ensure no tone. (If tone,
reduce resistor value 1 value) .
Solder R14 into place.
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5. ENGINEERING CHANGE NOTES RELEVANT TO HY-TRAK 100D
5.1 101 - Solves Drift and CMRR Adjustments
5.2 102 - Earth Bonding
5.3 103 - Modified DPM Unit
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SECTION 5 /PAGE 1
5 . ENGINEERING CHANGE NOTES RELEVANT TO 100D
5.1 ECN 101 - Drift & CMRR Adjustments
Problem :
Elongated setting up time due to:
(a) Selecting IC's 3, 4, & 5 for zero drift with volume.
(b) Setting up CMRR pot.
Solution for 1 :
(a) Remove IC's 3 and 4 and associated IC sockets.
(b) Replace resistors R21 and R22 with links.
(c) Link IC3.3 to IC3.2.
(d) Link IC4.3 to IC4.2.
(e) Wire IC4.1 to IC5.1 (also see (g) below).
(f) Wire IC4.5 to IC5.5 (also see (g) below) .
(g) Insert Tant. capacitor 2.2uf 16v between IC4.1 and IC4.5
(polarity immaterial) .
(h) Replace link idented -15V (near centre of PCB) with 470/1
l/4w 5% resistor.
(j) Replace C5 with lOuf 16V electrolytic capacitor (polarity
+ to 0V connection) .
(k) Cut track going to IC5 pin 4.
(1) Wire from new C5 cap -ve to IC5.4.
(m) Remove existing loudspeaker earth wire.
Reroute from loudspeaker to 0V link (near centre of PCB)
or as close as possible to transformer 0V.
Solution for 2 :
(a) Replace R26 (9K La) with lOKn. 1% lOOppm resistor.
(b) Replace VRl with link.
No CMRR adjustment is now required.
5.2 ECN 102 - Earth Bonding
SAFETY WARNING TO ALL OMNITEST HY-TRAK 100D USERS
THE HY-TRAK 100D SHOULD NOT BE USED UNTIL THE FOLLOWING
MODIFICATIONS ARE CARRIED OUT.
Problem :
The front and rear panels of the HY-TRAK 100D are metal and are
not earthed. As such this constitutes a potential health hazard
and Omnitest Limited recommends that the following modifications
are made to each instrument immediately.
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SECTION 5 /PAGE 2
Solution:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(J)
(k)
(1)
(m)
(n)
(P)
(q)
(r)
Disconnect the instrument from the mains supply.
Remove the probes from the front panel.
Remove 4 countersunk screws from the base of the instrument.
Lift off the lid and sides of the case complete with the
handle .
Remove knob from on/off volume pot. (This simply pulls off.)
Unscrew the nut now revealed and slide on/off volume pot to
the rear. It is not necessary to unsolder the wires to this
pot.
Add one 3/8" diameter solder tag to pot shaft, reposition in
front panel and retighten retaining nut. We recommend the
application of zinc paste to the front panel to prevent future
oxidisation of the connection.
Unsolder the Earth, Live and Neutral wires from the rear of
the printed circuit board, adjacent to the mains transformer.
Remove the rear panel. Drill and countersink a 4ba clearance
hole in a suitable position.
Solder a 4ba solder tag to themains earth wire (yellow/green) .
Solder a yellow/ green wire in 16/0.2 gauge of suitable length
to the earth point on the PCB. Terminate in a 4ba solder tag.
Solder a yellow/green wire in 16/0.2 gauge of suitable length
to the 3/8" solder tag on the on/off volume pot. Terminate
in a 4ba solder tag.
Bolt these three solder tags to the rear panel using a 4ba x i"
countersunk screw, shakeproof washer and nut. Again the use
of zinc paste on the rear panel is recommended.
Resolder the Live (brown) and Neutral (blue) wires to the L
and N terminals on the PCB. The connections should be sleeved
with silicon rubber or heat-shrink sleeving.
Replace the loudspeaker retaining screw situated near the
centre of the PCB, with a M3 x 20mm countersunk nylon screw.
Do not overtighten.
Replace lid being careful to slide the front and rear panels
into the appropriate grooves. Replace the 4 countersunk
screws in the base.
Replace the probes, reconnect the instrument to the mains and
check the instrument still functions correctly.
This modification scheme should not affect the calibration of the
instrument at all.
NOTICE
If you do not wish to carry out this modification yourselves,
.the instrument should be returned, suitably packed and post paid,
to Omnitest Limited, where we shall be pleased to modify your
instrument free of charge. There will, however, be a small fee
to cover the return post and packing of the instrument.
The instrument should be clearly labelled 'Returned for earth
modification' .
RESTRICTED AND COMMERCIAL IN CONFIDENCE
ISS.l SECTION 5/PAGE 3
5.3 ECN 103 - Modified PPM Units
This ECN only applies to any unit that had to use an Anders OEM2
to replace an OEM1 DPM.
Problem :
The OEM2 when used as a direct replacement for the OEMl causes
a high current drain on the +4.7V supply.
Dl, D2 and D3 inputs control the decimal point position on the
LCD. These are actually inputs to a CMOS 4070 chip on the
Anders OEM2. This chip has VDD at +4.7V (i.e. direct from our
HY-TRAK +4.7V supply) but we now discover that VSS is not
connected to -4.7V but to its own internal logic zero rail
(about -2V) . Thus when we drive Dl , D2 or D3 to our logic zero
of -4.7V, we are applying a negative voltage below the VSS of
the chip which is turning on the input protection diodes and
causing the high current drain on the VDD supply.
Solution :
We must connect pin 7 of IC10 and the -ve rail to switches 3 and
4 of the HY-TRAK to the logic zero rail of the OEM2.
This involves 2 track cuts and two links to be fitted.
The logic zero rail of the OEM's is available at the 'TEST'
connection of the 0EM2. This is linked to the TST pin of the
HY-TRAK.
Rl and R2 on the HY-TRAK should now be lKn. - this gives us a
potential 10mA supply which is ample for the 0EM2 and IC10 under
normal conditions.
Mod . Scheme :
1. Cut track at IC10 pin 7.
2. Cut -4.7V rail between switch 3 and VS pin.
3. Link TST pin to IC10 pin 7 and switch 3 formerly -4.7V rail
pin.
Application :
(a) This mod scheme should be applied to all HY-TRAKs fitted with
OEM2's, i.e. Serial No. 1110 onwards.
(b) Any older unit that has to be repaired with a new DPM.
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